calculations

[Tom Macaulay]

Hi, PANO helpers;  I use an iMAC, OS 10.5:
   Can someone help me on a perplexing problem?
    I have a datafile with 8 fields, P; I; S; R; N; R1; R2; R3;. All are
numeric money fields except N which is numeric only.  I use the
EQUATION area in the DESIGN SHEET, Spreadsheet Mode, and for field S, I
enter P*I;, for field R, I enter P+S.  Calculations are proper.
However, if I enter either of these equations, or any other equation,  
for fields R1, R2, or R3, no calculations are performed.  However, if  
I change the "R"  fields to other names, such as A, B, D, calculations  
perform properly.  In other words,  calculations fail if the last  
three field are similar.  This does not seem right.
   Can someone point out the error of my ways ?
Tom, Reno.